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Telephoto lens vs Telescope

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I have a good quality 500mm zoom lens for my Nikon D200 and I've got a Celestron piggy-back mount for my NextStar 6se.

Couple of questions:-

a. Is mounting the lens and camera on the piggy-back mount going to strain the motors of the NextStar?

b. How will the image quality of the telephoto lens be compared to using a t-adaptor on the scope. I think that the magnification of the telephoto will be about (500/40) 12x, not sure what it will be with the scope ?

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The Nexstar 6SE uses the same mount as the 8SE, so it shouldn't have any problem if your lens + camera does not weight more than 1.1kg (weight differences between C6 and C8 OTA). However, assuming your 500mm zoom is the Bigma, the combine weight of it and your D200 will be near 3kg, which is close to half the loading capacity of a GP2.

The C6 OTA has a focal length of 1500mm so it will give you a magnification of around 1500/35=43x on a D200.

I am quite interested in that piggy mount myself for use with DSLR and shorter prime lenses, but it looks rather weak for mounting a large telephoto.

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If the NexStar SE mount is the same fittings as the SLT mount, you could just get yourself a dovetail bar and mount the camera to that. Then remove the scope, fit your camera and away you go. If the NexStar mount isn't on a wedge, then you will be limited in exposure time depending on where in the sky you are aiming. From 2 minutes, low in the east or west, down to about 30 to 40 seconds North/South or at the Zenith.

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The key thing, I think, is that trying to go unguided with a whopping 1.5 metre focal length is unrealistic but the camera lens is more promising. I would say that at 500 mm focal length even on a well aligned wedge you will be lucky to get beyond two minutes. I would aim to back the zoom right off and go for wider fields more tolerant of tracking error. 500mm is a telescopic focal length, longer by 50mm than my Tak FSQ. You will have plenty of wonderful targets, believe me.


Edited by ollypenrice
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